I couldn't help thinking of some of Malaga Bay's postings when coming across this at http://phys.org/print303991846.html … a piece of research on amber deposits. A team of sicentists have analysed modern and fossil resins and the results seem to suggest there was less oxygen in the atmosphere in the geological past than previously imagined. The study therefore raises a question mark about current theories on the evolution of climate and of life itself, including the causes of gigantism in dinosaurs.
Scientists obviously have a problem when trying to reconstruct atmospheric composition in the earlier history of the Earth because of a lack of samplingt material. That doesn't stop them guessing though, and strutting their guesswork. Now we have a study of an organic material that has preserved reliable data – fossil resins. Amber has the advantage of remain chemically and isotopically almost unchanged – in spite of polymerization. Over 500 amber samples were analysed, from a variety of different periods, and oxygen concentration was half the rate thought to be. They also found that low oxygen levels coincided with high carbon dioxide concentrations.